In most of the known sphygmomanometers the manometer is contained in a usually cup-shaped case and is mounted therein on one of the parts of the case. This case also contains the dial through which the meter shaft passes. Above the dial the pointer is mounted on the meter shaft. The dial, and the pointer are covered by a crystal which is either inserted directly on the upper margin of the case or is inserted in a separate bezel which in turn is joined to the margin of the case (EP-A-0 008 351 A2). In both cases the disk seals the interior of the case, with the parts contained therein, from the exterior.
If such a sphygmomanometer falls onto a hard surface there is the danger that the case may be damaged, especially that it may be distorted. In the area of the bottom, and of the transition from the bottom to the circumferential wall, the case has of its nature a comparatively great stability of shape, so that in this area the distortions caused by dropping generally remain comparatively slight. It is different when the case strikes in the area of its top margin where the dial and the crystal become damaged. The dial may be bent or may bulge. Such deformation of the dial can be so great that the pointer can no longer move across the dial.
If the case becomes deformed the dial may also snap out of its mounting. The same applies to the crystal. In the event of a particularly hard shock the spiral return spring of the manometer mechanism may become damaged, when for example one or more of its coils loop over one another and become entangled. In the case of all such damage or even destruction of individual parts, the entire sphygmomanometer becomes useless.